How to import a large number of product classes and attributes from a file?

Preparing for Siebel 8.1.1.3 deployment, we need to enter a large number of products, product classes and attributes to Siebel. The products, classes and attributes are currently specified in an Excel file. While there is an option to enter all the data manually, it would take many man-days. Currently, we are planning to load the basic product information using EIM. But how to load product classes and attributes?

Can we use any existing automation to load classes and attributes, which are not coming from another Siebel installation? For example, is there a particular way to prepare an XML that could be then loaded using Workspace Projects View? Or any other way?